1. Field of the Invention
The present invention relates to an insert nut, and more particularly, to an insert nut having a diamond lattice structure and a manufacturing method thereof, in which a melted portion of a base material is settled on a settlement protrusion, when installing the insert nut, thereby increasing binding force between the base material and the insert nut.
2. Description of Related Art
Generally, a screw member has been widely used when assembling two members into one unit. Recently, an insert nut which is integrally injection-molded with a product is used in electronic products which are required to be thinner. For example, most mobile phone covers or bodies are formed into a two-divided case, and the insert nut is provided by press fitting or insert-injection molding in order to facilely assemble electronic parts in the case.
The insert nut is one kind of fastening mechanism for fixing one part to the other part, in which a member having a predetermined hole and formed of a resin material is fixedly installed in order to improve trouble forming a threaded hole in a body or housing, thereby allowing a screw or bolt having a predetermined diameter to be screwed.
The insert nut is injected into a hole of a housing fixed by a jig. Herein, the insert nut is heat-welded instantaneously by using high-frequency current and then bonded by a press bonding tool. In the instantaneous heat-welding, process temperature thereof is varied according to the kind of used base material in which the insert nut is installed. Typically, the insert nut is heated to a temperature of 300° C. or more and then pressed into an installation hole of the base material.
Therefore, the internal circumferential surface of the installation hole of the base material is melted by the heated insert nut and then welded among multiple protrusions formed on the external circumferential surface of the insert nut, thereby achieving the bonding between the base material and the insert nut.
In Korean Patent Laid-Open Publication No. 10-2009-0057498, there is disclosed “an insert nut and a manufacturing method thereof” in which a plurality of settlement protrusions are formed at the external surface of the insert nut so as to be provided along a screw thereof. Hereinafter, it will be described detailedly with reference to the drawings.
FIG. 1 is a view showing a conventional insert nut. As shown in FIG. 1, the insert nut 2 includes a cylindrical insertion part 12 of which an internal circumferential surface 4 is tap-processed and an external circumferential surface is formed with a plurality of settlement protrusions 10 that are formed by a plurality of horizontal and vertical grooves 6 and 8 so as to be protruded in the form of a lattice, and a flange part 14 which is integrally formed with one end of the insert part 12. Each edge portion thereof is chamfered. Especially, an front end of the insertion part 12, which is inserted into the base material, is rounded so as to be facilely inserted into the base material.
The settlement protrusions 10 are defined by the horizontal grooves 8 formed in a direction orthogonal to a length direction of the insertion part 12 and the vertical grooves 6 formed in the length direction thereof. The insertion part 12 may be inserted into or separated from the base material by a screw motion. If necessary, the horizontal grooves 8 may be substituted with a left-handed or right-handed screw. Further, the horizontal grooves 8 may be a single screw thread, a double screw thread or a triple screw thread.
The inner and outer surfaces of the flange part 14 are formed into a circular shape. However, in order to rotate the insert nut with a spanner or a wrench, the inner surface thereof may be formed with a hexagonal or polygonal groove, or the outer surface thereof may be formed into a hexagonal or polygonal shape.
Since a depth and caving angle of the vertical and horizontal grooves 6 and 8 is determined in accordance with the conventional insert nut, the description of shapes and dimensions thereof will be omitted. If the depth of the grooves 6 and 8 is large, binding force with the base material M is increased, and if the depth thereof is shallow, it is reduced.
Further, the insert nut 2 consists of the cylindrical insertion part 12 and the flange part 14 which is integrally formed with one end of the insertion part 12. Firstly, a cutting process is carried out, in which a prepared round rod is cut into a unit length, thereby forming a unit round rod. A length of the unit round rod is appropriately determined within the range that a press working can be performed. Then a punching process is performed, in which a basic outer shape and internal circumferential surface of the insert nut is formed by using a press punch.
In the punching process, the unit round rod may be formed with a complete bolt hole, and each edge portions may be chamfered. The bolt hole for forming the internal circumferential surface 4 of the insertion part may be completely formed through the precise punching process having two or more steps, or may be formed by a single punching process. Accordingly, it is possible to massively produce the insert nut which can be facilely installs in the base material.
However, in the conventional insert nut as described above, the lattice thereof is arranged in the form of a rectangle, and the grooves are formed longitudinally or transversely between the lattices. Therefore, when the insert nut is installed, the melted portion of the base material may be flowed down between the lattices, and thus the deposition efficiency between the insert nut and the base material is reduced. That is, the insert nut having the rectangular lattice can be facilely produced, but the melted portion of the base material is not deposited sufficiently between the lattices due to the arrangement of the lattices.
In practice, a pull out force of the insert nut having the rectangular lattice, which is being used currently, is about 600˜650 kgf, and thus it is necessary to increase the pull out force in order to satisfy the international standard specification.
The applicant tested the pull out force of the conventional insert nut having the rectangular lattice, and a typical injection material for a vehicle, such as PA66-GF35 and PA6-GF30, was used as the base material. The testing result is shown in FIG. 5.
As shown in FIG. 5, a unit of the pull out force is kgf, and an ultrasonic heating temperature with respect to the insert nut is 300˜350° C. As shown in the drawing, the average pull out force of the base material formed of PA66-GF35 is 634 kgf, and the average pull out force of PA6-GF30 is 628.1 kgf. As shown in the result, the pull out force of the insert nut having the rectangular lattice is included within the range of the Korean standard specification, but inferior to the international standard specification for overseas export market.